Microelectromechanical Systems (MEMS) sensor devices are widely used in applications such as automotive, inertial guidance systems, household appliances, protection systems for a variety of devices, and many other industrial, scientific, and engineering systems. Such MEMS devices are used to sense a physical condition such as acceleration, pressure, or temperature, and to provide an electrical signal representative of the sensed physical condition. Capacitive-sensing MEMS sensor designs are highly desirable for operation in high gravity environments and in miniaturized devices, and due to their relatively low cost.
Many MEMS sensor device applications require smaller size and low cost packaging to meet aggressive cost targets. In addition, MEMS device applications are calling for lower temperature coefficient of offset (TCO) specifications. TCO is a measure of how much thermal stresses effect the performance of a semiconductor device, such as a MEMS device. A high TCO indicates correspondingly high thermally induced stress. The fabrication and packaging of MEMS device applications often uses various materials with dissimilar coefficients of thermal expansion. As the various materials expand and contract at different rates in the presence of temperature changes, the active transducer layer of the MEMS device may experience stretching, bending, warping and other deformations due to the different dimensional changes of the different materials. Thus, significant thermal stress, i.e., an undesirably high TCO, often develops during manufacture or operation.
In addition, stresses can result from soldering the packaged MEMS device onto a printed circuit board in an end application. These package stresses can change the strain of the substrate on which the MEMS sensor is mounted causing offset shifts, or displacements. Moreover, the substrate may undergo some non-constant strain such as non-uniform stretching, bending, or warping across a surface of the substrate. The displacement induced by package stress and substrate strain can cause changes in the sense signal, thus adversely affecting the output performance of the MEMS device.